1. Field of the Invention
The invention relates to a high-surface-area, high-activity granular media for liquid filtration and/or treatment. More specifically, the preferred embodiment relates to a two-part media composition of binder and active particles, without a conventional solid support core. The media comprises binder-agglomerated active materials, wherein a binder material holds together particles of active component so that a high percentage of the active particles are exposed to the liquid being filtered/treated. The granules may take the faun, for example, of an inner core and/or matrix of binder that supports an active component coating, or the form of active particles bound together by particles, globules, or amorphous shapes of binder.
2. Related Art
Particulate materials have been disclosed for removal of heavy metal contaminants from aqueous solutions and vapor phase systems, for example, in Lisenko (U.S. Pat. Nos. 5,639,550 (“'550”) and 5,603,987 (“'987”)). Lisenko '550 illustrates in FIG. 1A a prior art media, such as found in U.S. Pat. No. 5,277,931, in which a porous particle (S) is first sprayed with an aqueous basic material (B) and subsequently sprayed with a concentrated aqueous acidic solution of a source of suitable metallic ions. The sprayed-on source of suitable metallic ions is the primary material (P), that is, the active material. Such spray-on prior art media are described by Lisenko as exhibiting high attrition.
Lisenko discloses a particulate media comprising three-part granules (G′, FIG. 1B), wherein each granule is made of a large support material (S), and a primary material (P) bound to the outer surface of the support material by a binder material (B). In Lisenko, the softening temperature of the binder is less than the softening temperature of the support material and less than the softening temperature of the primary material. Thus, Lisenko discloses a three-part composite, wherein the center core is a solid particulate that holds two layers on its outer surface, an intermediate layer of binder and an outer layer of primary filtration material. In other words, the three-part media is a solid support with a solid primary material “stuck” to the support by a layer of binder that is relatively very thin compared to the diameter of the support material.
In three-part granules, the support material preferably has preferably substantially uniform particle diameters which are substantially greater in size than the particle diameters of the primary material. The support material may be granulated activated carbon, glass beads or bubbles; porous or non-porous volcanic media; plastic beads or pellets; plastic fibers; wood fibers; carbon fibers; ceramic media; fired or unfired clay; diatomaceous earth; metal particles; ferro magnetic material; silica gel; magnetic stainless steel; organic fiber; cellulose fiber; acrylic fiber; and silicon carbide.
The primary material for the three-part granules may be inorganic hydrated metal oxides, amorphous metal silicates, zeolite and mixtures thereof, and more preferably inorganic hydrated titanium oxides or silicates, inorganic hydrated tin oxides or silicates and mixtures thereof, and most preferably titanium silicate, tin silicate and mixtures thereof, and most preferably titanium silicate, tin silicate and mixtures thereof. The primary material is chosen for a desired property for treatment, such as ion exchange capacity or metals removal. Preferably, the primary material may be micronized or powdered in form.
The binder in a three-part granular media is chosen from a wide variety of materials including crystalline thermoplastic polymer, thermoplastic polymer, crystalline polymer and mixtures thereof, preferably polyolefins, polyamides and mixtures thereof, and specifically polyethylene, polypropylene, ethylene vinyl acetate and mixtures thereof. The binder material may be provided in particulate form to the process of manufacturing the composite media.
Typical relative sizes for the components of three-part granular are illustrated in FIG. 5A. The large support particles are shown in the 4-100 mesh range (from very large particles down to 140 microns), the primary particles are shown in the 230-500 mesh range (approximately 60 down to 25 microns) and binder particles are shown in the 450-500 mesh range (approximately 30 microns and smaller).
During manufacture of the three-part granular media, the primary particulate, binder particulate, and support particulate are mixed and the mixture is heated to a temperature within about 25 degrees of the softening temperature of the binder material. This way, the binder material does not soften to the point where it readily flows and masks the internal pores of the primary and support materials. This procedure causes the binder material to lose shape and become sufficiently viscous to adhere the primary particles to the support material, with the binder in-between. Then, the mixture is cooled to ambient whereby adhesion of the binder material between the primary material and the support material becomes substantially permanent. The result is a particulate media with particles having diameters generally equal to the diameter of the support material plus the layers of binder and primary material.
Still, there is needed an improved particulate filter/treatment media that is strong, very high in active surface area, and economical and convenient to make and use. The present invention serves these needs.